Method of making refrigerating apparatus



Sept. 9, 1958 E. F. SCHWELLER ETAL 2,850,793

METHOD OF MAKING REFRIGERATING APPARATUS 2 Shets-Sheet 1 Filed March 20, 1953 IN V EN TOR.

Fig. 3

Edmund F. .ScfiweI/er 5 By Charles CEW/rist/er Jr.

IE. W.

The/r Affarney- Sept. 9, 1958 E. F. SCHWELLER EIAL I 2,850,793

METHOD OF MAKING REFRIGERATING APPARATUS Filed March 20, 1953 2 Sheets-Sheet 2 i. A F/ .8

6 2. 9 IN VEN TOR.

Edmund Ff .Schwsl/er Mb/r Attorney BY Char/es C. Whistler Jr.

United States Faten 2,850,793 Patented Sept. 9, 1958 METHOD OF MAKING REFRIGERATING APPARATUS Application March 20, 1953, Serial No. 343,616 1 cram. or. 29 -1573 This invention relates to refrigerating apparatus and more particularly to an improved form of heat exchange coil which may be used either as a condenser or an evaporator in a volatile refrigerant system. g w

it is an object of this invention to provide an improved heat exchange coil which may be manufactured at a low cost.

Another object of this invention is to provide a new method and apparatus for manufacturing low cost heat exchangers. 7

Still another object of this invention is to provide a flat tube type of heat exchanger which is capable of withstanding high internal pressures and which is efficient in operation.

Further objects and advantages of the present invention will be apparent from the following description, r eference being had to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.

in the drawings:

Figure l is a perspective view showing a strip of metal used in forming the heat exchanger tube;

Figure 2 is a perspective view showing the strip folded back on itself;

Figure 3 is a perspective view of a mandrel used in bending the flattened tube into serpentine shape;

Figure 4 is a perspective view of the serpentine tube;

Figure 5 is a plan view of a forming fixture used in dilating the tube shown in Figure 4;

Figure 6 is a vertical sectional view through the forming fixture;

Figure 7 is a somewhat similar vertical sectional view taken at right angles to the view in Figure 6;

Figure 8 is a fragmentary end elevational view with parts broken away to show the relationship between the tube and the fins;

Figure 9 is a fragmentary side view with parts broken away of one of the heat exchangers embodying the invention; and,

Figure 10 is a fragmentary perspective view showing the relationship between the fins and the tubing in a finished heat exchanger.

Referring now to the drawing wherein a preferred embodiment of the invention has been shown, reference numeral 20 designates a strip of metal such as aluminum, copper or steel which has been sand blasted on its one side as indicated at 21 and passed between forming rollers to crease the strip as shown at 22, 24 and 26. After the strip has been thus creased, it is bent into the shape shown in Figure 2 with the sand blasted side placed inside. It will be noted that the creases 22 and 26 are spaced inwardly from the outer edges a sufficient distance that these outer edges overlap one another beyond the curve-d portion formed by the creases 22 and 26. The thickness of the metal strip itself is so small that it is desirable to form a joint in this manner so that the mating surfaces at the joint have a greater area of contact than the area of the edges of the strip itself. Some of the material in these overlapping edges is used in arc welding the edges of the folded strip as indicated at 28. Thus, a portion of the material in the overlapping edges of the strip itself forms the necessary fillet at the welded seam. 'The Welding is performed in an inert gas atmosphere in accordance with standard practice.

The flat strip of metal, after having been welded along its edge as shown at 28 in Figures 2 and 3, is also welded shut at its ends and is provided with inlet and outlet tubes 36 and 38 as shown. After the strip is thus sealed, it is bent into serpentine shape with the aid of a forming mandrel 36. This forming mandrel is provided with a curved end portion 32 which has been cut away as indicatedat 34 intermediate the edges of the curved portion. The bending of the tube tends to distort the walls of the tubing at the bends as the inner radius is shorter than the outer radius. The cut away portion 34 provides a localized space into which the surplus material of the inner radius of the bent tube may project. It has been found desirable to retain the surplus material at the return bend preferably in the form of a single crease in the material. This crease automatically extends in a direction substantially perpendicular to the edges of the tube as a result of providing the above mentioned cut away at 34.

The serpentine tube is next inserted into a forming fixture generally designated by the reference numeral 40. This forming fixture consists of a number of blocks which provide between them a serpentine passage 42 into which the serpentine tube 44 in Figure 4 may be inserted It will be noted that certain of the blocks 46 constitute What may be called inside radius forming elements and other blocks 48 constitute what may be termed outside radius forming elements which serve to back up the outer walls of the tube at the bends in the tube. The forming blocks 46 and 48 are mounted between heavy plates 50 and 52 which engage the edges of the flattened tube when. thetube is expanded. The usual knockout pins 53 are carried by the base plate 55 which also supports one or more guide rods 57. Suitable spacer blocks such as blocks 5? are provided as shown and may be removed so as to shorten the serpentine passages.

The expansion of the tube is accomplished by injecting a fluid into the tube through the inlet 36 while the main tube is held in the forming fixture. This expansion fully opens the passages and flattens the side walls of the tubing. The creases 22 and 26 being located adjacent the welded seam reduce the strain on the seam during the expansion process.

it will be noted that the inside radius forming blocks 46 are provided with cut away portions or slots 47 into which the inner radius of the flattened tube is free to expand as indicated at 47 in Figure 9 of the drawing. By virtue of this arrangement, it is obvious that the return bends of the expanded tube do not offer any restriction to the flow of fluid.

Pressures approximating 2000 pounds per square inch are used so as to expand the tube into the shape shown in Figures 8, 9 and 10. Before the expansion takes place the flattened tube as shown in Figure 2 may have outside dimensions of .080 inch thick by 2% inches wide whereas after the expansion has taken place, the tube dimensions are approximately .200 inch by 2 /2 inches wide. (The dimensions given herein are for purposes of illustration only and may be varied within reason.)

Upon completion of the expansion process, the serpentine tube is removed from the forming fixture and a series of fin units 6% having A inch perforations 61 formed therein are placed adjacent opposite sides of the tube Walls as shown in Figures 8, 9 and 10. In addition to the fins 60, channel elements 62 are placed adjacent the edges of the tubes as best shown in Figure 8. These channel elements 62 have a width equal to the thickness of the tube and have wide flanges which engage the flat portions of the fins 60. The tubing, fins and channels are then brazed to one another so as to form a composite structure wherein the channel 60 serves to hold adjacent fin assemblies in proper spaced relationship at all times. The brazing operation may be done in various manners, thus ribbons of brazing material (not shown) may be placed between the walls of the tubing and the fin assemblies or the fins and/ or the tubing may be made from material precoated with a brazing material so that when the assembly is heated the fins will be brazed onto the side walls of the tube and onto the sides of the channels 62. The channels 62 then serve to prevent the adjacent fin assemblies from spreading and this in turn prevents the walls of the flat tubing from bulging in response to high internal pressures.

As shown in Figure 9, a relatively heavy mounting plate 70 may be used at the ends of the heat exchanger. These mounting plates are cut away as indicated at 72 so as to provide apertures through which the return bends of the fiat tube 44 may pass. As indicated in Figure 9, the ends of the channels 62 may he formed with ears 74 which may be bent over onto the mounting element 70 as shown so as to assist in holding the elements in assembled relationship during handling prior to the brazing operation. The mounting bracket 70 has purposely been omitted in Figure so as to more clearly show the relationship between the channel 62, the fins 60 and the flattened tubing 44.

By virtue of the above described construction and method of manufacture, a heat exchanger having high efficiency is provided. The sand blasted interior surface materially increases the efficiency of the unit and the perforations in the fins facilitate the drainage of condensation from the fins when the heat exchanger is used as an evaporator.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, as may come within the scope of the claim which follows.

What is claimed is as follows:

The method of forming a multiple pass heat exchanger having integrally formed return bends therein which comprises forming longitudinally extending grooves adjacent the edges of a strip of fiat stock and then folding the strip along its center line, bonding the edges together to form a flat conduit, bending the stock at spaced intervals to form a plurality of parallel passes joined by integrally formed return bends, thereafter supplying fluid pressure internally of said conduit while limiting the extent of outward movement of the walls of said conduit so as to dilate said conduit a predetermined amount, forming transverse corrugations in metal strip material so as to form corrugated fin strips, attaching said fin strips on the opposite flat sid s of each of said passes, and tieing the end portion of the tin strips on one side of each pass to the end portion of the fin strips on the opposite side of the pass so as to prevent separation of the fins on opposite sides of said passes and thereby prevent bulging of the flat side walls of the con duit.

References Cited in the file of this patent UNITED STATES PATENTS 1,753,435 Klocke Apr. 8, 1930 1,861,448 Murray June 7, 1932 2,190,494 Templin Feb. 13, 1940 2,195,259 Ramsaur Mar. 26, 1940 2,211,813 Franco-Ferreira Aug. 20, 1940 2,271,538 Brace Feb. 3, 1942 2,427,336 Askin Sept. 16, 1947 2,462,511 Kramer Feb. 22, 1949 2,582,358 Schoellerman Ian. 15, 1952 2,605,731 Schulze et al. Aug. 5, 1952 2,649,067 Kranenberg Aug. 18, 1953 2,656,146 Sollinger Oct. 20, 1953 2,673,542 Smith Mar. 30, 1954 2,686,957 Koerper Aug. 24, 1954 2,794,243 Schweller June 4, 1957 2,804,285 Peterson Aug. 27, 1957 FOREIGN PATENTS 747,064 Great Britain Mar. 28, 1956 

